When a process is executing, its message loop is in a wait state. The message loop executes every time a Windows message is sent to the process by the operating system. Calling CloseMainWindow sends a request to close to the main window, which, in a well-formed application, closes child windows and revokes all running message loops for the application. The request to exit the process by calling CloseMainWindow does not force the application to quit. The application can ask for user verification before quitting, or it can refuse to quit. To force the application to quit, use the Kill method. The behavior of CloseMainWindow is identical to that of a user closing an application's main window using the system menu. Therefore, the request to exit the process by closing the main window does not force the application to quit immediately.

Data edited by the process or resources allocated to the process can be lost if you call Kill. Kill causes an abnormal process termination, and should be used only when necessary. CloseMainWindow enables an orderly termination of the process and closes all windows, so it is preferable for applications with an interface. If CloseMainWindow fails, you can use Kill to terminate the process. Kill is the only way to terminate processes that do not have graphical interfaces.

You can call Kill and CloseMainWindow only for processes that are running on the local computer. You cannot cause processes on remote computers to exit. You can only view information for processes running on remote computers.

The following example starts an instance of Notepad. It then retrieves the physical memory usage of the associated process at 2 second intervals for a maximum of 10 seconds. The example detects whether the process exits before 10 seconds have elapsed. The example closes the process if it is still running after 10 seconds.